Piotr Nowojski created FLINK-12912:
--------------------------------------

             Summary: Incorrect handling of task.checkpoint.alignment.max-size 
when one checkpoint subsumes another one
                 Key: FLINK-12912
                 URL: https://issues.apache.org/jira/browse/FLINK-12912
             Project: Flink
          Issue Type: Bug
          Components: Runtime / Network
    Affects Versions: 1.8.0, 1.7.2, 1.6.4
            Reporter: Piotr Nowojski
            Assignee: Piotr Nowojski


{{BarrierBuffer#numQueuedBytes}} which is used to evaluate {{ 
task.checkpoint.alignment.max-size}} limit, is not correctly handled if one 
checkpoint subsumes another one.

The max size limit is checked against a sum of {{numQueuedBytes}} and 
{{bufferBlocker.getBytesBlocked()}}. The {{getBytesBlocked}} keeps tracks of 
the alignment size of the only most latest checkpoint. The bug is 
{{BarrierBuffer#releaseBlocksAndResetBarriers()}} method, where while handling 
first subsumed checkpoint in the branch:

{code:java}
                if (currentBuffered == null) {
                        // common case: no more buffered data
                        currentBuffered = 
bufferBlocker.rollOverReusingResources();
                        if (currentBuffered != null) {
                                currentBuffered.open();
                        }
                }
{code}

we clear the {{bufferBlocker.getBytesBlocked()}} counter, while we do not 
update {{numQueuedBytes}} counter. 

For example when first checkpoint approached to 99.9% of max alignment size 
when it was subsumed, due to this bug calculated alignment size drops to 0 
bytes. For subsequent subsumed checkpoints {{numQueuedBytes}} is correctly 
updated.



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